Introduction to the Flora of the Exchange Lands at Aldersbrook

A survey of the plant life of the old Sewage Works Site was undertaken and the results published in the 1996/97 issue of The Essex Naturalist *. A total of 237 of flowering plant species were listed in the report. Part of that report is reproduced here, slightly updated, looking at the various areas that comprise the site and the plants that were found.

The Plants of the Sewage Works

One of the main approaches to the site is via Empress Avenue, off Aldersbrook Road in the Aldersbrook area of Manor Park. (photo) As the last of the houses in Empress Avenue is passed, the road becomes more of a track - although well surfaced these days since it became part of the London Cycle Network (LCN). The track winds between allotments and the land used by the local riding school, downhill towards the Roding. Near the entrance to the riding school is the original vehicle entrance to the sewage works. (click here for map)

The 8.5 Acre Site (Areas 1, 2, 3, 3a)

The 8.5 acre site, comprising areas 1, 2, 3, 3a on the map of the area, is the western part of the original sewage works, separated from the rest by the a "field" which was believed to be owned by the London Borough of Redbridge but is, apparently, owned by Thames Water Authority.

The original vehicle access point to the works from Empress Avenue was a large locked gate, but is now just a locked single bar barrier but with access for pedestrians, cyclists and - if permitted - horses.

Area 1. Turning left through the gate from Empress Avenue, towards nearby Wanstead Park, the western boundary of the site is a concrete fence behind which is a riding school and stables.This north-west corner of the site has been designated Area 1 and has much great sallow Salix caprea caprea developing beside the more mature trees. The mature trees here are nearer the fence and include pedunculate (common or English) oak Quercus robur and sycamore Acer pseudoplatanus. There are some grassy mounds on which grow some large hawthorn Crataegus monogyna, annual meadow grass Poa annua, and foxglove Digitalis purpurea. A small amount of spring beautyMontia perfoliata did grow here, but has not been seen in recent years. Broom Sarothamnus scoparius also occurs, and a small amount of lesser celandine Ranunculus ficaria. There is a patch of grassland here too, at the edge of which was some dyer's greenweedGenista tinctoria, a plant which is not known in the Forest nearer than Pole Hill at Chingford; unfortunately encroaching vegetation seems to have overtaken this plant as it has not been found in the last few years. In the grassland was also found sickle medick Medicago falcata, and spotted medick Medicago arabica. The willow and thicker shrub layer that has encroached includes brambleRubus fruticosus and Japanese knotweed Polygonum cuspidatum .

The boundary between the Area - and indeed the whole of the site - and Wanstead Park to the north is an earth bank of some 2 or 3 metres height surmounted until late 1993 by a high wire fence. The fence has now been removed, and the bank has become something of a footpath. Trees grow both on and either side of much of the bank, forming a shelter between the open aspect of the sewage works and the more wooded nature of the Park. Many of these trees are either mature or more commonly sapling sycamore, and also hawthorn. There are some pedunculate oaks, large and small specimens of wild cherry Prunus avium, some elm Ulmus sp. suckers, and much elder Sambucus nigra. There are one or two seedling horse chestnuts Aesculus hippocastanum at the eastern end, probably from a mature tree by the Ornamental Waters in the Park. Just on the sewage works side of the bank can be found bluebells Endymion non-scriptus, ground ivyGlechoma hederacea, hogweedHeracleum sphondylium, cleavers Galium aparine, red dead-nettle Lamium purpureum, white dead nettleLamium album, and a small patch of cuckoo pint Arum maculatum.

Area 2 comprises the area south of the access track that runs through the site and is bordered to the west by the concrete fence that continues southwards from the access gate towards the City of London Cemetery. Behind the fence are the Aldersbrook Allotments belonging to the London Borough of Redbridge. A line of shrubs including blackthornPrunus spinosa were planted here in April 1994 to act as a more natural and pleasing boundary. Near the main entrance gate is a large crack willow Salix fragilis and plants such as bramble forming a scrub area. Beyond this to the east of the fence, the greater part of Area 2 is quite an open aspect. In the early stages of the site's development, there was masses of hemlockConium maculatum here, with large patches of nettle Urtica dioica. In 2007, there are various members of the pea family - medics and trefoils - and also both goat's-beardTragopogan pratensis and salsifyT. porrifolius. It may well be that the latter originated from the nearby allotments, and probably hybrids occur.

Towards the centre of Area 2 was a system of eight rectangular concrete enclosed drying pans. Though a slightly different flora had developed in each of these, generally they included prickly lettuceLactuca serriola and great lettuce L. virosa, and the smooth and the prickly sow-thistles Sonchus oleraceus and S. asper growing in the rough materials that made up the base of the beds. In 1992 some shining cranesbillGeranium lucidum was noted sheltered close against the concrete edge of a drying pan; in 1993 there was masses of this species, which is almost unknown elsewhere locally. When the concrete was removed, the shining cranesbill disappeared from here. The concrete walls also had a selection of lichens adding to the interest, but the expertise was not available to identify these.

Immediately to the north of the drying pans, open grassland graded into the compacted foundations of buildings or road. The grassland has become almost meadow-like, with a colourful display of plants including clovers Trifolium spp., vetches Vicia spp.; yarrowAchillea millefolium as well as some hybrid daffodils Narcissus spp., teaselDipsacus fullonum, mugwortArtemisia vulgaris and wormwood Artemisia absinthum. Of particular interest is a colony of grass vetchlingLathyrus nissolia. It was plants such as this that it was hoped might be retained when the site was to be made suitable to become part of Epping Forest. It has been decided to refer to this area as "Ted's Meadow" in memory of the late Ted Godden, who helped with recording the wildflowers and particularly liked this area. Closer to the access track, a single specimen of bladder senna Colutea arborescens was present for many years - favoured by the cattle that occasionally found there way into the site - but after the area was used for storage of materials being used for re-surfacing in adjacent Wanstead Park, the plant has been destroyed. Also present is a small but good specimen of Midland hawthornCrataegus oxyacanthoides. Most other hawthorns in the surroundings are C. monogyna. There is also apple Malus sp., a laburnumLaburnum anagyroides, dog roseRosa canina and some large patches of bramble. In 1998, a colony of bee orchidsOphrys apifera was was found near here, but in 2007 only two plants (photo) could be found amongst the rank grassland that is developing.

Returning to the west boundary fence of the site, there is a locked access gate from the allotments where the southern boundary is met. Though the City of London Cemetery is just a few feet away, it is separated from the old sewage works by a public footpath known as "the Bridle Path", either side of which iron railings form the boundary of both the cemetery and the sewage works, which also has a hawthorn hedge. The path is also the boundary between the London Boroughs of Newham and Redbridge.

A wooded embankment accompanies much of the length of these railings with something of the remains of an old track from the allotments still in evidence, though almost impassable due mainly to bramble. It was felt that calling this area "Sadie's Wood" might be appropriate; in memory of Jennifer Charter's little whippet Sadie who liked to follow me through part of this wood! The trees are a mixture of mature and seedling sycamore, some oak, some silver birch Betula pendula and also hawthorn, holly and elder. A single seedling yew Taxus baccata was found - about one foot high in early 1994. Much of this wood has suffers from having been used apparently as a rubbish tip in the past, and this continues to accumulate in the form of litter being blown in from the Cemetery. This is a problem around the cemetery, particularly here and on the eastern edge where what could otherwise be a very pleasant path is to some extent spoilt in this way. In recent years, the cemetery authorities have put up some chicken-wire - particularly at the N.E. corner of the cemetery - which does alleviate the problem to some extent. However, possibly also originating from the cemetery, the wood has a number of hybrid daffodils Narcissus spp. to brighten things up in the spring. Bramble and nettle constitute much of the undergrowth with lesser celandine, ivy speedwell Veronica hederifolia, a patch of broom Sarothamnus scoparius, a small amount of ivy Hedera helix, and annual meadow grass Poa annua.

The boundary graded for some years into the Redbridge (or Thames Water Authority) Field by a four metre wide strip of un-mown grass requested of the London Borough of Redbridge, who maintained it, by the Wren Group. However, the grass-cutting regime on the field eventually reverted to cutting too close to the hawthorn patches which had developed along the boundary which, together with bramble, could allow nesting sites for birds including long-tailed tit Aegithalos caudatus. After 2008, this cutting regime ceased and the area is now developing a very different plant community. (see "Redbridge Field", below)

At the northern end of the field, the western edge of Area 3 is wooded, and as such has much in common with the adjacent part of Wanstead Park. Near to the entrance to the sewage works from Wanstead Park there is a specimen of locust treeRobinia pseudoacacia. The next nearest known tree of this species occurs by the Dell Bridge, nearby in Wanstead Park. It may also be remarked that something of an avenue of limes Tilia vulgaris lead from the adjacent Park into the sewage works site, suggesting an historic landscaping link between the two areas. At the southern edge of the wooded area is a large specimen of lilacSyringa vulgaris. Between the wooded area and the field were the remains of clinker beds. Little plant growth had obtained a footing on this, though bramble was spreading and specimens of whitebeam Sorbus aria existed. In 2007 a single specimen of vervain Verbena officinalis was found. On the grassy verge between here and the Redbridge Field dark mulleinVerbascum nigrum and great mullein or Aaron's rod Verbascum thapsus was present, although this area was severely affected in 2008/9 by works which involved digging a borehole and then boring a water-pipeline into Wanstead Park. In 2010 about nine spikes of the dark mullein were evident, comprising of two or three separate plants.

Area 3a, south of the clinker beds, was an area comprising both the foundation of buildings and what appeared to be an old basement in the form of a large walled pit. A number of plants associated with gardens were found here, such as snow-in-summer Cerastium tomentosum and balm Melissa officinalis, as well as trees and shrubs which were to be retained after the development works. These included a dogwoodThelycrania sp., cherry-laurel Prunus laurocerasus, buddleia Buddleja davidii, and a wild cherry. A quantity of common horsetailEquisetum arvense grew along the edge of the pit, but is now declining, and some shining cranesbillGeranium lucidum became established in 1993. Associated with the trackway nearby are such plants as whitlow grassErophila draba, hairy bitter-cressCardamine hirsuta, creeping cinquefoilPotentilla reptans, tall melilot Melilotus altissima, white melilot Melilotus alba and wall pepperSedum acre, as well as mosses and lichens.

In the grassland between here and the filter beds are two patches of lesser celandine, weld Reseda luteola and much hoary cressCardaria draba.

Redbridge Field

The plant life here is that commonly associated with a rough lawn, such as daisy Bellis perennis, greater plantainPlantago major,ribwort plantainP. lanceolata and dandelionTaraxacum officinale. There is a strong population of spotted medickMedicago arabica. On the bank separating it from the bridle path the vegetation is less disturbed and here may be found fennel Foeniculum vulgare,ox-eye daisyChrysanthemum leucanthemum, meadow vetchling Lathyrus pratensis and hairy tare Vicia hirsuta.

A now well established hawthorn edge on the eastern edge of the field separates this part of the Sewage Works Site from the 11 acre or Wilderness area. During 2008, much of this land was disturbed by Thames Water Authority to establish a bore-hole intended to carry water to the Redbridge Water Treatment works. In doing so, some plants of dark mullein Verbascum nigrum which grew along the boundary of the Epping Forest part of the site were destroyed. By September, the work had temporarily ceased although much of the area was still enclosed by a metal fence and a variety of equipment, pipes, hard-surfacing etc. was scatttered around. On the disturbed soils a variety of plants had appeared. These included a lot of common fumitoryFumaria officinalis and - on an earth-mound - a specimen of thorn-appleDatura stramonium. In early 2009 work re-commenced, with considerable heavy equipment on-site to install a pipeline from the borehole northwards into Wanstead Park. This was undertaken by using a machine called the "Longbore" (photo).

After the pipeline work was completed, the Redbridge Field had changed considerably. There was now a fenced area with two large containers within it, and outside of the enclosure to the east a hard surface had been put down. Some of the area - as well as having the grass stripped away - had also accumulated chippings from surfaces used for temporary buildings and vehicles. The grass had no longer been cut, and much disturbance had taken place, so that a variety of plants had been allowed to grow or had possibly been accidentaly introduced. By the Spring of 2010 the spontaneous growth of plants gave the area a feel of what much of the Sewage Works site had soon after it was seeded in the early 1990s. A colourful display of wild-flowers were to be enjoyed throughout the summer, with particular emphasis perhaps on the weld Reseda luteola which was much enjoyed by insects.

The 11 Acre or "Wilderness" area (Areas 4, 5, 6)

Areas 4, 5 and 6 are also known as the 11 acre or "Wilderness" area and are separated from the Park on the north by a similar bank to that described earlier. Its western edge, from this bank southward to the bridle path, was originally a wire fence with stiles as at the other side of Redbridge's field, but by 2000 was a substantial hawthorn hedge. The northern edge was again a wire fence, but with a metal access gate from their roadway. Both the wire fence and the metal gate had almost disappeared by 2000.

The wilderness area in 1994. Leaning on the gate are Ted Godden and Paul Ferris. (Photo by Jennifer Charter)

As on the other side of the field, the difference between the mown grass of Redbridge Field and that which has developed in the works is extreme. A track serves to differentiate Areas 4 and 5: west of the track has been designated Area 4 and east of the track Area 5. Area 4 is mostly rank grassland with some patches of bramble, elder and increasingly crack willow. Until the hardcore track was laid to facilitate work on the overhead power-lines here in early 1994, there was a very attractive grassy track. In 2000 the track still had not regained the appearance it had, and some of the hardcore was treacherous. Only by 2005 had it returned to something like its original aspect, and it wasn't until about 2008 that the rubble that had been used had become naturally infilled enough for comfortable walking.

Area 5. The track is bounded on its eastern side by an old hedge which now consists mainly of elder running from the park end of the works, separating the grass from an old sludge lagoon which has become Area 5. The lower parts of the area - which was the sludge lagoon proper - particularly in its southern half, is quite rank vegetation The northern end has been graded downwards from the level of the track which passes the site here by use of an infertile topsoil of sandy gravel. This has given rise to a relatively sparse and less rank vegetation than the southern half of the lagoon There is grass interspersed with flowering plants and these have included bee orchidOphrys apiferaand pyramidal orchidAnacamptis pyramidalis. In 2008 a single plant of firethornPyracantha coccinea was noted. Well established, this may be another case of a plant that has been there for some time - but not noticed! Butterflies and other insects favour this area, and it can be quite attractive in Summer. The rank vegetation of the southern end includes cleavers Galium aparine, nettle Urtica dioica, cow parsley Anthriscus sylvestris and hemlock, with a number of patches of elder. Giant hogweedHeracleum mantegazzianum was noted in 1998. This is the largest of the European herbaceous plants - the stem can be up to 4m tall - and both the stem and the leaf contain chemicals that can cause painful blistering. It is a very invasive species, typically found near riversides. Its presence here - although impressive - is unwelcome. The spread of this plant was noted during the following years in a pattern that has been seen so many times elsewhere. In this case the tendency was to follow the eastern boundary of Area 5, and increasingly move west. In 2010 a serious effort was made by the City of London to try to deal with it, although the exact methods used are not known.

Area 6 is bounded to the east by the River Roding while the western edge consists of an old concrete fence which acted as a barrier between the works and the bridle path by the City of London Cemetery, though the fence is now in a very poor state as is the bridle path. Where the sewage works area narrows to its southern-most end there is just a short length of fence and a large metal gate - now left open - and then the River Roding which forms the entire eastern boundary. A large part of the area adjacent to the concrete fence was another sludge lagoon, again with much hemlock. Whilst the works was in use it was common to see many brown rats Ratus norvegicus hereabouts, but also more attractive visitors such as whinchat Saxicola rubetra and stonechat Saxicola torquata might pass through on migration. Similarly, kestrels were often seen, but not so often now (2011). However, the area is much used by a variety of smaller birds including common whitethroat Sylvia communis. Common comfreySymphytum officinale is a common plant here, as is hare's-foot cloverTrifolium arvense.Another plant which has gained a hold here since the renovation is crow garlicAllium vineale.

The remains of a tarmac track served to separate Area 6 from the grassy banks leading down to a grass track by the river. The tarmac track and the soil that grades into it provide a habitat for a variety of low plants such as wall pepper creeping cinquefoil, and whitlow grassErophila draba. Also growing alongside are a variety of bushes and shrubs including brambleRubus fruticosus agg., dewberry Rubus caesius, cut-leaved bramble Rubus laciniatus and elder, as well as hawthorns and silver birch. One or two plants of great mulleinVerbascum thapsus also occur beside this track and just away from the track, in the grassy areas, white campionSilene alba.

The grass covered embankment forms part of the river defences of the Roding. Here is found squirrel tail fescue Vulpia bromoides, not otherwise known locally, as well as barren brome Anisantha sterilis, soft brome Bromus mollis, meadow foxtail Alopecurus pratensis, and Yorkshire fog Holcus lanatus.

The River Roding

The River Roding - with its source near Molehill Green in Essex and its confluence with the Thames at Barking - forms the entire eastern boundary of the sewage works, and as such its plant life needs to be included in this survey.

From the new bridge across the river at the work's north eastern corner (from which, it may be noted, flounders Platichthys flesus may be seen), a tree covered embankment winds alongside the river, separating it from what was a sludge lagoon to the west. This provides a very pleasant wooded walk, with views of the nearby river. The tree and shrub cover consists of much hawthorn, though their are some large crack willow Salix fragilis, and bramble and ivy tend to invade so as to hinder passage. While the works was in use, tree sparrows Passer montanus were often seen here, but no longer.

The river itself - although not easy of access - does have some mud and shingle banks, depending on the depth of the river. A plant that does get established here is water figwort Scrophularia aquaticum. Where the tree covered bank ends about midway along the riverside boundary of the works, a grass track continues with a much more open aspect of the river. At about this point, bulrush Schoenoplectus lacustris is present in the river and further south, a small muddy island had formed by the mid 90's and had developed a plant community which has included brooklime Veronica beccabunga and, increasingly, great reedmaceTypha latifolia. Increasingly over the years the island was colonised by more dominant species, the narrow channel on the west side became shallower, until by 2010 it was only an island at all at times of particularly high water-levels. From various viewpoints along the length of the Roding between Manor Park and Redbridge, some significant meanders may be seen, and this sequence over something like ten years was a good example of how a river changes its course as new "land" is developed after a shingle or mud bank becomes colonised. An example of this can be seen by comparing the following photograph - taken in 2011 - with the one above which was taken in 2000; a tree has grown on what was little more than a shingle bank.

In Spring coltsfootTussilago farfara is common, and in early summer much of the river bank is brightened by masses of wild turnip or bargeman's cabbageBrassica rapa ssp. campestris. Later lucerne Medicago sativa is much in evidence. Himalayan balsam Impatiens glandulifera is another invasive plant that is increasing in this location - in 2008 just a small amount was present actually within the sewage works site - much more being outside to the south, but by 2010 it was evident that the plant had gained a strong foothold on stretches of the river-bank in the sewage works. At the southern end of the sewage works a metal gate - which now remains permanently open - gives access to and from a riverside walk that continues to join the Alders Brook as far as the railway lines from Liverpool Street station.

In 2007, a tarmac track was created as part of the Roding Valley Cycle Route, from the railway bridge through to this point. It is regrettable that this track has been routed to end exactly at this entrance to Epping Forest, when a perfectly good alternative was available using the nearby bridle-path. This will only encourage unnecessary disturbance of the Exchange lands site, where - as can be seen - such a wealth of wildlife exists. The view from the river bank from just beyond the gate, particularly looking north towards Wanstead Park, is surprisingly rural for east London, and spoilt only by the overhead power-lines. Finally, from this viewpoint and looking across to the opposite bank of the river with the golf course beyond, there are one or two examples of water dock Rumex hydrolapathum growing on the bank by the river, a plant not recorded elsewhere hereabouts.